Thermoplastically processable aromatic polyether amide
The invention relates to thermoplastically processable aromatic polyether amides laving a high heat distortion point, their preparation via solution or melt condensation, and their use for the production of shaped articles, filaments, fibers, films and coatings.
Aromatic polyamides are a known class of high performance polymers (Coprehensive Polymer Sci. Vol. 5, page 375 (1989), Encyclopedia of Polymer Science Vol. 11, page 381 (1986); U.S. Pat. Nos. 3,063,966; 3,671,542 and GB 1,246,168).
Aromatic polyamides are generally highly crystalline polymers which often cannot be melted without decomposition and which lave high glass transition temperatures. They have excellent mechanical, thermal and chemical properties. The aromatic polyamide of terephthalic acid and p-phenylenediamine (formula 1) ##STR2## thus has very good mechanical properties and is comparable to steel on a weight basis.
However, an essential disadvantage of these materials is that they are very difficult and expensive to process. Because of the high crystallinity, the melting point (about 550.degree. C.) is far above the decomposition temperature (about 350.degree. C.), so that thermoplastic processing by standard techniques such as extrusion or injection molding is not possible.
The only possible method is therefore processing to give fibers or films from solution. Aggressive media, such as concentrated sulfuric acid, chlorosulfonic acid or nitrogen-containing solvents, such as N-methylpyrrolidone or dimethylacetamide with considerable additions of salts (up to 6% by weight) are often the only media which can be used for this purpose (DE-A-22 19 703). The content of inorganic concomitant substances, determined by ash analysis, is typically several thousand ppm in this process (C. O. Pruneda, R. J. Morgan, R. Lim, J. Gregory, J. W. Fischer, "The Impurities in Kevlar 49 Fibers", SAMPE Journal, Sept./Oct. 1985, 17).
A better solubility can be achieved by incorporation of meta-linkages, for example by reaction of isophthaloyl chloride with m-phenylenediamine (U.S. Pat. No. 3,063,966). Although these polyamides (formula 2) ##STR3## have a better solubility, they cannot be processed thermoplastically.
Thermoplastic processing is an essential prerequisite for wide use as a polymeric material.
In DSC (differential scanning calorimetry), amorphous polymers exhibit a glass transition temperature which indicates the start of cooperative chain mobility. Just above the glass transition temperature, however, the viscosity of the melt is so high (&gt;10 000 Pa.s), that processing by injection molding or extrusion is not possible. Only as the temperature increases further does the melt viscosity fall to the values necessary for this processing. The processing range for amorphous polymers is typically at least 100.degree. C. above the glass transition temperature, for example polyether sulfone having a glass transition temperature of 225.degree. C. is processed by injection molding at 340.degree.-360.degree. C.
Partly crystalline polymers exhibit a melting peak in DSC, in addition to a glass transition point. Processing via the melt is therefore possible only above the melting point. The processing temperatures are typically about 10.degree.-50.degree. C. above the melting point.
The desired decrease in melt viscosity can be achieved--above all in the case of amorphous polymers--by increasing the temperature. However, this is counteracted by the limited thermal stability of the polymers. Although polymers can often be converted into the liquid state by increasing the temperature, processing from the melt is thus not always implicitly associated with this. For processing via injection molding or extrusion under the usual conditions in practice, it is necessary for the material to undergo practically no change in melt viscosity, for example by degradation or crosslinking, over a prolonged period of time at the processing temperature.
There has been no lack of attempts to prepare fusible polyamides which have high glass transition temperatures and good mechanical properties (high elasticity too dull, good tear and penetration strengths) and which furthermore allow thermoplastic processing by the standard techniques.
Aromatic polyamides which have flexibilizing ether groupings in the diamine portion, are capable of flow and can be shaped in the melt are described in DE-A-26 36 379 (U.S. Pat. No. 4,278,786). The flowability of an aromatic polyamide of isophthaloyl dichloride, terephthaloyl chloride and 2,2-bis 4-(4-aminophenoxy)phenyl!propane, which has a reduced viscosity of 0.81 dl/g, is thus 5.6.times.10.sup.-3 cm.sup.3 /s at temperatures in the range from 250.degree. to 300.degree. C. under a load of 300 kg. However, processing of these polymers with the aid of injection molding or extrusion techniques at such low flowabilities cannot take place.
Structural variations (incorporation of meta-linkages) lead to no increase in flowability (DE-A-26 36 379, Examples 2, 3, 4, 5; Comparison Example E of this application). Interface condensation for the preparation of such polyamides leads, by partial hydrolysis, to carboxyl and amino groups which are located on the ends of the polymer chain and are reactive in the melt.
Aromatic polyamides and polyacrylates which can be processed from the melt are described in EP-A-263 593.5-tert-Butylisophthalic acid is employed as the acid component. The disadvantage of the materials described here lies mainly in their inadequate heat resistance, since the aliphatic side chain tends to undergo side reactions at higher temperatures, leading to a drastic change in melt viscosity.
Thermoplastically processable aromatic polyether amides which, for example, can be pressed or ram-extruded to give sheets are furthermore known (DE-A-38 18 208 (U.S. Ser. No. 357 527) and DE-A-38 18 209 (U.S. Ser. No. 358 180)). Solution condensation of the aromatic dicarboxylic acid chloride with the aromatic diamine is carried out using equimolar amounts in aprotic, polar solvents of the amide type. Chain-blocking agents, for example monofunctional amines or benzoyl chloride, are already added during the polymerization operation, i.e. in the presence of the diacid chloride, to limit the molecular weight.
Premature ending of the polymerization operation occurs in this manner, only half of the end groups reacting with the chain-blocking agent and the other half remaining reactive. A comparable effect occurs if one or two different chain-blocking reagents are added after the maximum possible molecular weight which can be achieved experimentally has been reached (Comparison Example C of this application).
The intrinsic viscosities of these polymers lie in a range from 1.5 to 4 dl/g, which corresponds to melt viscosities of more than 10 000 Pa.s, at below the decomposition temperature. Here also, processing by injection molding or extrusion is therefore not possible (see Comparison Example B of this application).
The invention is based on the object of developing thermoplastic aromatic polyether amides which can be processed by injection molding or extrusion processes and have good mechanical properties.
The aim of the present invention is therefore to provide, from favorable starting components, aromatic polyamides which have a high glass transition temperature and excellent mechanical properties and can be processed thermoplastically, with the proviso that the aromatic polyamides form stable melts, have melt viscosities of less than 10 000 Pa.s at below the decomposition temperature and can be processed by injection molding or extrusion.
Another aim of the present invention is to provide a process for the preparation of aromatic polyamides which leads to products having a reproducible molecular weight and stable melt viscosity properties.
Another aim of the present invention is to provide a process for shaping filaments, fibers, films and moldings by thermoplastic processes, preferably injection molding or extrusion.